IP Pass-through mode

As per sthe suggestion of @Brackan, i tried his suggestion and indeed, the modem exposes the IP of the first machine to connect (which is not the expected behaviour as it should expose the IP provided by the ISP). The issue is that to do a factory reset, you must use the UI and therefore connect a device and after reset, the modem restarts in "router" mode, hence it does DHCP server. And, you cannot enable IP pass-thru from the modem screen… so kinda in a dead-lock… Any idea ?

Thanks